Various solid freeform fabrication, or SFF, techniques are commonly used to produce three-dimensional objects. The various approaches are generally characterized by the building up of three-dimensional objects from computer data descriptive of the object in an additive manner from a plurality of formed and adhered layers, each layer representing a cross-section of the three-dimensional object. Typically, successive layers of the object are formed and adhered to a stack of previously formed and adhered layers. According to one SFF technique, an object cross-section is formed by selectively depositing an unsolidified, flowable material onto a working surface in desired patterns which will become part of the object cross-section, and then allowing or causing the material to form the object cross-section and simultaneously adhere to a previously-formed object cross-section. These steps are then repeated to successively build up the three-dimensional object cross-section by cross-section. This approach is referred to as selective deposition modeling (SDM) due to the manner in which object formation occurs.
Typical SDM approaches include Thermal Stereolithography as described in U.S. Pat. No. 5,141,680 to Almquist et al. Also typical of this approach is Fused Deposition Modeling as described in U.S. Pat. Nos. 5,121,329 and 5,340,433 to Crump in which a thermosettable material is dispensed while in a molten state and then hardens after being allowed to cool. Another example is described in U.S. Pat. No. 5,260,009 to Penn. Another example is Ballistic Particle Manufacturing as described in U.S. Pat. Nos. 4,665,492; 5,134,569 and 5,216,616 to Masters, in which particles are directed to specific locations to form object cross-sections.
Thermal stereolithography is particularly suitable for use in an office environment because non-reactive, non-toxic materials can be used. Moreover, the process of forming objects using these materials may not require the use of radiations (e.g. UV radiation, IR radiation and/or laser radiation), heating materials to combustible temperatures (e.g. burning the material along cross-section boundaries), reactive chemicals (e.g. photopolymers) or toxic chemicals (e.g. solvents & the like), complicated cutting machinery, and the like, which can be noisy or pose significant risks if mishandled. Instead, object formation is achieved by heating the material to a flowable temperature then selectively dispensing the material and allowing it to cool.
A critical problem that exists in relation to thermal stereolithography and the like involves finding suitable materials that are capable of being dispensed from the dispensers currently used in such systems (such as an ink jet print head), and which are also capable of forming three-dimensional objects with suitable strength and accuracy once they have been formed. In addition, build materials must be paired with particular support materials to provide the necessary mechanical support for the three-dimensional object to be accurately produced yet allowing for the finished object to be conveniently and safely separated from the support material after the SDM process is complete.
Pattern waxes suitable for use in investment casting are generally not suitable for SDM processes. These materials tend to have high viscosities, relatively low toughness, or other properties which makes them difficult to handle and dispense from multi-orifice ink-jet dispensers such as those which may be used in SDM processes. High material viscosity also reduces the ability to build accurate parts. Previous pattern waxes in the appropriate viscosity range typically exhibit relatively high layer to layer distortion. Further, these previous materials tend to have latent heat properties that are not suitable for quick heat dissipation and fast three-dimensional object building.
For these and other reasons, there is an unmet need for materials suitable for use in SDM which are capable of being jetted through an appropriate dispenser (such as multi-orifice, ink-jet type print head) and have the toughness, handling, and dimensional stability properties appropriate for selective deposition modeling. These materials should also have the properties sufficient for the subsequent use of the three-dimensional object, for example, as a pattern for investment casting processes.